1. Field of the Invention
The invention is in the field of programmable elements and pertains to a programmable element and to a memory device containing a plurality of such programmable elements as memory elements or a logic circuit containing such programmable elements as programmable logic elements.
2. Description of the Related Art
Non-volatile memory devices in two-terminal and three-terminal geometries have been provided by the use of so-called programmable-resistance materials based on Transition Metal Oxides (TMOs). An example of such memory devices has been disclosed in U.S. Pat. No. 6,815,744. In such a memory device, electrical pulses of opposite polarity can switch the resistance reversibly and persistently between a low-resistance state and a high-resistance state. However, memory cells based on this technology have been found to exhibit a large statistical spread of the resistance values, both in one cell and from cell to cell. Also, the endurance is limited.
Another class of programmable elements is the components used in programmable logic devices or PLDs. Unlike a logic gate based on CMOS, which has a fixed function, a programmable element of a PLD has an undefined function at the time of manufacture. Before the PLD can be used in a circuit it must be programmed. A PLD element can be considered as a combination of a logic element and a memory element. As memory elements or switches, antifuse devices, EEPROMs, solid-electrolyte switches or phase-change memories are used. The PLDs, such as the FPGA (field-programmable gate arrays), have more flexibility than fixed logic gates, can be re-programmed to fix errors and have a shorter time-to-market. However, FPGAs are generally slower than their application-specific integrated circuit (ASIC) counterparts, draw more power and are less area-efficient due to the combination of logic and memory elements.
Therefore, it is desirable to provide a programmable element that is suitable of serving as non-volatile memory element with a reduced influence of statistical spread on read operations and/or with an increased endurance compared to prior art non-volatile memory cells. It is further desirable to provide a programmable element suitable as memory element with increased information density. It is even further desirable to provide a programmable element that is suitable as a logic element of a non-volatile programmable logic circuit.